Not sure if I have to fix the fabbot.io error, because I didn't change that line.

In the issue itself, you say yourselves

The value of the ChoiceQuestion array should not be NULL, but I can happen

I think you should rather fix your code to avoid passing null

IIUC from the issue 3 => null, is the problem, and im wondering why SA tools arent telling us. Should we fix a phpdoc instead?

@stof I understand, but probably in PHP 8 you will get an error instead of a deprecation and developers might think the problem is in the Symfony core. But now I think more about this, maybe it's better to check if the value is a string or is stringable, otherwise throw an exception with "Must be string or stringable"? Didn't check, but probably you can also pass a integer (that will work as long as isn't strict), object or array.